Two police officers have serious burns as a result of a gas bottle explosion at a Melbourne flat that also injured four others.

Police were called to a Middle Park flat on Saturday after reports of a man threatening self-harm. As firefighters and police entered the flat via the balcony using a ladder, there was a large explosion caused by an exploding gas bottle.

The intensity of the explosion shattered the windows of the apartment.

Police Deputy Commissioner Tim Cartwright said police believed the incident to be a suicide attempt rather than a malicious attack.

"This is probably the worst nightmare we have," Cartwright said. "I find this a tragedy, it cuts very deep.

"Our members deal with people with mental illness every day ... You ask them to go and look after the community and as a result, this happens."

Cartwright said the relatives of the police officers were traumatised by the event.

Two junior female officers who had been in the job fewer than four years received serious burns to their faces and upper bodies and are in serious but stable conditions after surgery at the Alfred hospital.

A male sergeant in his 50s is in a stable condition at the hospital.

Two firefighters were hospitalised with non-life-threatening injuries. One was released from hospital on Saturday night, while the other remains at the Royal Melbourne hospital in a stable condition.

A 40-year-old male resident remains in a serious but stable condition at the Alfred hospital and is under police guard. Police said the man was not in a fit state to talk but could face charges.

Cartwright said a medical practitioner had offered assistance at the scene to spray the injured police officers using a garden hose.

Psychologists, welfare officers and a police chaplain will speak to the police officers and their families.

Police will remain at the crime scene until Monday to investigate.

Victoria's acting premier, Peter Ryan, offered his condolences on behalf of the state government.

"Our thoughts are with the police officers so seriously injured, and also with the firefighters who were badly burned, in this terrible incident," Ryan said.

He said the tragedy draws attention to how working as a police officer can be dangerous.

"We wish them a complete recovery. On behalf of the Victorian government, I thank them for the vital role which they play in protecting all of us," he said.

* Readers seeking support and information about suicide prevention can contact Lifeline on 13 11 14 or Suicide Call Back Service 100 659 467.